1. Field
The disclosed embodiments relate to a method to determine the total temperature of the air stream surrounding an aircraft, especially when the aircraft is on the ground. The determining of the total temperature, according to the method of the disclosed embodiments, takes account of the measured values of the static temperature and the measured values of the total temperature.
The disclosed embodiments find application in aeronautics, especially in the measurement of parameters such as the parameters of air temperature outside the aircraft.
2. Brief Description of Related Developments
On board an aircraft, it is important to have certain items of information on the flight of the aircraft and especially the air temperature outside the aircraft. The air temperature outside the aircraft is measured by means of dedicated probes or multi-functional probes placed in the external structure of the aircraft. The external air temperature of the aircraft is generally given by the total temperature and by the static temperature. The total temperature is the temperature of the air stream around the aircraft in the presence of an air flow acting on the value of the temperature. The static temperature is the temperature of the air stream surrounding the aircraft under conditions such that the air flow has no influence on its value.
The total temperature is classically measured by one or more probes situated in the air flow and the static air temperature is computed from the measured values of the total temperature. The probes used to measure the total temperature are generally either autonomous probes dedicated to the measurement of temperature or probes associated with other sensors to form multi-functional probes. Whether autonomous or multi-functional, the probes are installed on board the aircraft, outside the aircraft, in an environment subjected to the air flow.
Since the external air temperature is extremely low, especially in flight, the probes are generally heated in order to prevent them from getting iced. In particular, in the case of multi-functional probes, de-icing is automatically set up as soon as the engine is started up. However, the heating of the probes necessarily entails an emission of heat. This heat may disturb the measurements by the probe, under certain conditions.
More specifically, when the aircraft is in flight, the air stream flowing around the probe dissipates the de-icing heat. The effect of the de-icing, i.e. the heating of the probe, can then be characterized and can therefore be corrected. In this case, the probe gives a precise and consistent total temperature. However, when the aircraft is on the ground, there is no air stream or hardly any air stream around the aircraft. The heat from the heating of the probe therefore cannot be removed. This heat from the heating is therefore taken into account by the probe and the total temperature measurement is therefore falsified.
To resolve this problem, it is possible not to de-ice the total temperature probe except beyond a certain speed of the air flow. The probe would therefore not be de-iced so long as the aircraft is on the ground. However, in this case, the measurements of total air temperature on the ground would depend on weather conditions. Indeed, in the event of snow or intense cold, when the aircraft is one the ground there is a risk that the probe might get iced and that the values measured by the probe might be erroneous. Furthermore, the probe would also be subjected to temperature differences directly related to exposure to the sun. Now differences in temperature due to climatic conditions cannot be characterized and therefore cannot be corrected.
Thus, whatever the de-icing conditions chosen (de-icing the probe solely off ground or de-icing the probe permanently) current measurement techniques do not provide for a reliable measurement of the total air temperature on the ground.